Collection History and Comparison of the Interactions - Forest Service

Collection History and Comparison of the Interactions of the Goldspotted Oak Borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), with Host Oaks in Southern California and Southeastern Arizona, U.S.A. Author(s) :Tom W. Coleman and Steven J. Seybold Source: Coleopterists Bulletin, 65(2):93-108. 2011. Published By: The Coleopterists Society DOI: 10.1649/072.065.0224 URL: http://www.bioone.org/doi/full/10.1649/072.065.0224

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The Coleopterists Bulletin, 65(2): 93–108. 2011.

COLLECTION HISTORY AND COMPARISON OF THE INTERACTIONS OF THE GOLDSPOTTED OAK BORER, AGRILUS AUROGUTTATUS SCHAEFFER (COLEOPTERA: BUPRESTIDAE), WITH HOST OAKS IN SOUTHERN CALIFORNIA AND SOUTHEASTERN ARIZONA, U.S.A. TOM W. COLEMAN USDA Forest Service, Forest Health Protection 602 S. Tippecanoe Ave., San Bernardino, CA 92408, U.S.A. [email protected] AND

STEVEN J. SEYBOLD USDA Forest Service, Pacific Southwest Research Station Chemical Ecology of Forest Insects 720 Olive Dr., Suite D, Davis, CA 95616, U.S.A. [email protected]

ABSTRACT An invasive population of the goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is colonizing and killing three species of oaks in San Diego Co., California. However, the interactions of A. auroguttatus with oaks in its native range in southeastern Arizona have not been recorded. We present a complete inventory of the North and Central American collection records of A. auroguttatus and Agrilus coxalis Waterhouse from the literature and from a survey of the holdings of 27 museum and personal collections. We also discuss the relationship between this collection history and the behavior of A. auroguttatus as an intracontinental invasive species. Surveys of native populations of A. auroguttatus in oak forest stands from four mountain ranges in southeastern Arizona revealed injury patterns on Emory oak, Quercus emoryi Torrey, and silverleaf oak, Quercus hypoleucoides A. Camus, similar to those observed on other “red” oaks in California. No damage was observed on “white” oaks in Arizona, and observed only rarely on a white oak, Quercus engelmannii Greene, in California. In Arizona, adult emergence was confirmed from bark removed from Q. emoryi, representing the first developmental record of A. auroguttatus from a native host. Late instars of Agrilus sp. were also recovered from Q. hypoleucoides, but they were not reared to the adult stage for species identification. Nonetheless, our observations of damage and the presence of larvae in the same configuration and location in the outer bark as we would expect for A. auroguttatus suggest that Q. hypoleucoides is also likely a host. Two hymenopteran parasitoids, Calosota elongata Gibson (Eupelmidae) and Atanycolus simplex Cresson (Braconidae), and two likely coleopteran predators (Trogossitidae and Elateridae) emerged from, or were collected in southeastern Arizona from, Q. emoryi bark infested with A. auroguttatus. Based on the museum survey results, the morphological similarity of individuals from the California and Arizona populations, the spatial dynamics of the pattern of infestation in California, the geographic isolation of hosts in California from native populations of the beetle, and the proximity of San Diego Co. to southeastern Arizona, we hypothesize that A. auroguttatus was introduced to California from Arizona or less likely from the Mexican states of Baja California, Chihuahua, or Sonora, and that the introduction most likely occurred on oak firewood. Further, we hypothesize that the oak mortality in southern California is occurring from this intracontinental invasive species because the beetle is filling a vacant niche by colonizing and developing in non-coevolved trees with low host resistance in the absence of a diverse and coevolved insect natural enemy complex. Key Words: Agrilus coxalis, Atanycolus simplex, Calosota elongata, firewood, intracontinental invasive species, oak mortality

Descanso Ranger District, Cleveland National Forest and Cuyamaca Rancho State Park (Fig. 1A–C). Until recently, this zone of oak mortality was not contiguous with the U.S.-Mexican border on its southern flank, but it now extends from the community of Campo in the southeast to Ramona in the northwest. In 2009, an additional isolated pocket of dying oaks was found at Marion Bear Memorial

Between 2002 and 2010, aerial survey data revealed an expanding pattern of extensive oak mortality on federal, state, tribal, and private lands in San Diego Co., California (CA). Approximately 21,535 coast live oaks, Quercus agrifolia Née (Fagaceae), California black oaks, Quercus kelloggii Newberry, and canyon live oaks, Quercus chrysolepis Liebm., have died in a 4,903 km2 area centered on the 93

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THE COLEOPTERISTS BULLETIN 65(2), 2011

Fig. 1. Distibution of oak mortality (red areas) caused by the goldspotted oak borer, Agrilus auroguttatus, in San Diego Co., California. A) 2002 to 2004, B) 2002 to 2007, C) 2002 to 2010. This area ranges from 32°42′09.90″N, 116°20′34.67″W to 32°49′41.60″N, 116°51′30.33″W to 32°36′31.45″N, 116°28′06.77″W to 33°11′58.64″N, 116°42′37.96″W. Location of satellite infestation (southwest of red * in map D) found in 2009 is Marion Bear Memorial Park near La Jolla.

Park near La Jolla, CA, on the edge of metropolitan San Diego to the west of the core area (Fig. 1D). Throughout San Diego Co., drought was considered the principal cause of this tree mortality for many years, and various pathogens have been suspected,

but never confirmed, as mortality agents. Tree mortality has been consistent over the past eight years and continues to spread from the area centered on the communities of Descanso, Guatay, and Pine Valley (Fig. 1A–C).


In June 2008, the goldspotted oak borer, Agrilus coxalis Waterhouse (Coleoptera: Buprestidae), was identified as the primary cause of this oak mortality (Coleman and Seybold 2008a, b). Hespenheide (1979) synonymized Agrilus auroguttatus Schaeffer (collected only in southeastern Arizona [AZ] at that time) with Agrilus coxalis (collected only in southern Mexico [Veracruz, Chiapas] and Guatemala at that time). However, given several morphological differences, the apparent disjunct nature of the distribution of the populations, and the morphological similarity of the specimens from the Arizona (AZ) (native) and CA (introduced) populations, Hespenheide and Bellamy (2009) assigned subspecific status to the AZ/CA (Agrilus coxalis auroguttatus Schaeffer) and Mexican/Guatemalan (Agrilus coxalis coxalis Waterhouse) populations. Most recently, Hespenheide et al. (2011) re-examined the species complex, and based on the male genitalia, they concluded that the AZ/CA and Mexican/Guatemalan forms do indeed comprise separate species with the original nomenclature (A. auroguttatus and A. coxalis, respectively). Westcott (2005) reported a specimen collected in southern Baja California, Mexico that is A. auroguttatus (Hespenheide et al. 2011). Life history data on any member of the species complex was absent prior to 2008 (Coleman and Seybold 2008b, 2010). Ground surveys in 2008 established that the distribution of A. auroguttatus in southern CA is contiguous with the zone of tree mortality. Observations documented through these surveys provided the first records of larval habits, host association, damage, and tree mortality associated with A. auroguttatus (Coleman and Seybold 2008b). Symptoms of infestation are wet, dark-colored stains on the bark surface, D-shaped adult exit holes through the bark, and reduction of foliage in the tree crown (Coleman and Seybold 2008a; Coleman et al. 2011; Hishinuma et al. 2011). Bark removed by foraging acorn, Melanerpes formicivorus (Swainson), and Nuttall’s, Picoides nuttallii (Gambel), woodpeckers (both Piciformes: Picidae) is also a common sign of infestation on Q. agrifolia. Agrilus auroguttatus attacks susceptible oaks aggressively along the main stem and largest branches, favors the lower bole, and rarely injures the upper branches. No additional insect species are associated with early A. auroguttatus injury in CA. The abundant A. auroguttatus larval galleries are dark-colored and form a meandering pattern on the wood surface. The larvae feed in the phloem and primarily on the xylem surface, and as a consequence, patches of cambium are killed, branches die back, and eventually trees die after several years of continuous infestation. Agrilus auroguttatus was first detected in southern CA in 2004 during an exotic wood borer survey by the California Department of Food and

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Agriculture (Westcott 2005). A preliminary survey of the collection history of A. auroguttatus and A. coxalis (Coleman and Seybold 2008b, 2009) revealed that A. coxalis was first recorded in the 1880s in Guatemala and southern Mexico, whereas A. auroguttatus was first recorded in the early 1900s in southeastern AZ. The species status of specimens collected in Costa Rica and Honduras remains unresolved (H.A. Hespenheide, personal communication). Thus, the species complex is native to North and Central America. Coleman and Seybold (2008b) presented two hypotheses for the newly recognized occurrence of A. auroguttatus in CA: 1) A. auroguttatus was introduced by human activity as a discrete population into southern California from its native range; or 2) A. auroguttatus expanded its range by natural dispersal from either AZ or Mexico (Westcott 2005). Herein we report the results of a more intensive survey of museum collections to document the complete historical distributions of A. auroguttatus and A. coxalis. We also report on the interactions of A. auroguttatus with oaks in southeastern AZ to document its behavior in its native range and provide more insight into its biology and population dynamics in CA. We discuss the most probable hypothesis for its introduction into CA and emphasize the potential impact of movement of oak firewood from within the current zone of infestation as a pathway for the accelerated expansion of the population of A. auroguttatus in CA.

MATERIAL

AND

METHODS

Museum Survey. We surveyed nine museum collections in CA and AZ and contacted three coleopterists in CA and Oregon with expertise in the Buprestidae (C.L. Bellamy, H.A. Hespenheide, and R.L. Westcott) for the holdings of A. auroguttatus and A. coxalis in their personal collections or their knowledge of holdings in other collections that we could not visit in person. Furthermore, we contacted 12 other major collections in the U.S. and Canada by e-mail for holdings of these species and reviewed the literature for other evidence of collection records. Determined and undetermined specimens of Buprestidae were surveyed in all collections that we visited in person. Label information was recorded for positively verified specimens. Data from museum collections were compiled with previously published information to determine the historical record of the A. coxalis complex in North and Central America. The following museum and personal collections were included in the survey. Acronyms (all USA unless otherwise indicated) are based on Evenhuis (2010). AMNH-American Museum of Natural History, New York, NY; BMNH-The Natural History Museum, London, UK; BPBM-Bernice P. Bishop

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Museum, Honolulu, HI; BYU-Provo, Brigham Young University, Monte L. Bean Life Science Museum, Provo, UT; CAS-California Academy of Sciences, San Francisco, CA; CHAH-Henry A. Hespenheide, personal collection, Los Angeles, CA; CIDA-College of Idaho, Orma J. Smith Museum of Natural History, Caldwell, ID; CLBC-Charles L. Bellamy–affiliated with CSCA; CMNC-Canadian Museum of Nature, Ottawa, Ontario, Canada; CNCI=CNC-Canadian National Collection of Insects, Ottawa, Ontario, Canada; CSCA-California State Collection of Arthropods, Sacramento, CA; EBCC-Universidad Nacional Autónoma de México, Estación Biológica Chamela, San Patricio, Jalisco, Mexico; EMEC-University of California, Essig Museum of Entomology, Berkeley, CA; FMNHField Museum of Natural History, Chicago, IL; FSCA- Florida State Collection of Arthropods, Gainesville, FL; GHNC- Gayle H. Nelson, personal collection, now in FSCA; LACM-Los Angeles County Museum of Natural History, Los Angeles, CA; MCZ-Museum of Comparative Zoology, Harvard University, Cambridge, MA; RHTC-Robert H. Turnbow, personal collection, Ft. Rucker, AL; RLWE-Richard L. Westcott, personal collection, Salem, OR; SBNM-Santa Barbara Museum of Natu-

ral History, Santa Barbara, CA; SDMC-San Diego Natural History Museum, San Diego, CA; TAMUTexas A&M University, College Station, TX; UAIC- University of Arizona Insect Collection, Tucson, AZ; UCDC-University of California, The Bohart Museum of Entomology, Davis, CA; UCRUniversity of California-Riverside, Riverside, CA; and USNM-National Museum of Natural History, Washington, DC. Field Survey in Arizona. Between December 2008 and October 2009, we conducted a ground survey of oak stands in four mountain ranges in the Coronado National Forest in southeastern AZ for recent oak mortality, in anticipation of linking mortality to the activity of A. auroguttatus (Fig. 2). Aerially detected hardwood mortality is not available for this region (USDA Forest Service 2010a), so comparison of long-term oak mortality between AZ and CA (e.g., Fig. 1) is not possible, but oak mortality can be described as occurring at latent levels in AZ. The native oak component in these four ranges is comprised primarily of Arizona white oak, Quercus arizonica Sarg., Emory oak, Quercus emoryi Torrey, Gambel oak, Quercus gambelii Nutt., gray oak, Quercus grisea Liebm., and silverleaf oak, Quercus hypoleucoides A. Camus.

Fig. 2. The four mountain ranges (Santa Catalina, Santa Rita, Huachuca, and Chiricahua) in the Coronado National Forest in southeastern Arizona where historical collections of Agrilus auroguttatus were made. General localities (X) are noted on the four mountain ranges, but a few exact localities ( ) were available from collection labels.

•


Arizona white oak, Emory oak, gray oak, and silverleaf oak are commonly found interspersed in the same forest stands at lower elevations (1,372– 1,981 m), whereas Gambel oak is restricted primarily to higher elevations (1,981–2,438 m). Field Survey in California. Between 2008 and 2010, we reared or hand-sampled A. auroguttatus and associated insects from logs of Q. agrifolia or Q. kelloggii, from standing trees in the Descanso Ranger District of the Cleveland National Forest or in William Heise County Park, Julian, CA. Between January and April 2010, recently killed Q. agrifolia were felled and logs were collected at Heise Park. Logs from the lower portion of the main stems from infested trees were quartered and placed into 1.8 × 1.8 m laboratory rearing cages (BioQuip, Gardena, CA). Cages were monitored for insect emergence from April to September 2010. The main stems of heavily infested and recently killed Q. agrifolia and Q. kelloggii were sampled by removing the outer bark and exposing the phloem at multiple locations in the Descanso Ranger District (Pine Creek Trailhead, Noble Canyon Trailhead, Glencliff Fire Station, Wooded Hills Campground, Pine Valley community, Descanso Ranger Station, and Laguna Mountain Recreation Area) and Heise Park. Agrilus auroguttatus and other insects were sampled from the standing trees from larval galleries and pupal cells of A. auroguttatus.

RESULTS Museum Survey. A total of 78 specimens (37 A. coxalis and 41 A. auroguttatus) collected prior to 2008 were recorded from museum collections and the literature (Table 1). The first collection of A. auroguttatus in CA is still represented by three adults collected in 2004 from San Diego Co. The museum survey revealed several new collections from Mexican states and U.S. mountain ranges, but no new records from Guatemalan departments when compared to previously reported localities (Waterhouse 1889; Schaeffer 1905; Fisher 1928; Hespenheide 1979; Westcott 2005; Coleman and Seybold 2008b; Hespenheide and Bellamy 2009). The new Mexican state records include one record of A. coxalis from Jalisco (Tuito, FSCA) and two records of A. coxalis from Tamaulipas (Santa Engracia, FMNH and Tula, USNM). The new U.S. records include four records of A. auroguttatus from the Chiricahua Mountains of AZ (CAS, FMNH-3) and two records of A. auroguttatus from the Santa Catalina Mountains of AZ (FSCA, UAIC). The two new Mexican state records represent a significant northward extension of the range of what we assume is A. coxalis on the Mexican mainland. There were no records of A. auroguttatus from Sonora or Chihuahua, immediately south of southeastern AZ.

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The survey confirmed that A. auroguttatus occurs in the Chiricahua Mountains of AZ (Cochise Co.) with one specimen collected in 1908 (CAS, Van Dyke personal collection) and several series of specimens collected between the early 1900s and 1957 (FMNH, J.N. Knull, personal collection). The collections from the Santa Catalina Mountains from Upper Bear Canyon (1965 and 1968) represent a new record for this mountain range, and the most northern collection in southeastern AZ (Pima Co.). Besides the Chiricahua and Santa Catalina Mountains, A. auroguttatus has been frequently collected from various canyons in two other mountain ranges of southeastern AZ (Huachuca and Santa Rita, Fig. 2). Thus, it is known from three counties in AZ (Cochise, Pima, and Santa Cruz Cos., primarily localities in the Coronado National Forest) and one county in CA (San Diego Co.); A. coxalis has been collected from nine states in Mexico and at least four departments in Guatemala. No specimens of A. auroguttatus or A. coxalis were found in any of the undetermined holdings from the collections in the survey. Two female specimens from the Honduran department of Olancho (FSCA) were also noted in the survey. They are likely A. coxalis, but future collection of males from this locality will be necessary to determine their relationship with Costa Rican specimens, which may represent a separate undescribed species (H. A. Hespenheide, personal communication). Field Survey in Arizona. During the detection survey, we observed D-shaped exit holes, meandering dark-colored larval galleries on the xylem surface, and pupal cells in the outer bark of several individuals of Q. emoryi and Q. hypoleucoides in canyons where historic collections of A. auroguttatus were made (e.g., Madera Canyon, Santa Rita Mountains, Pima and Santa Cruz Cos.; Miller and Carr Canyons, Huachuca Mountains, Cochise Co.; Pinery and Rucker Canyons, Chiricahua Mountains, Cochise Co.; and Willow Canyon, Santa Catalina Mountains, Pima Co., Fig. 2, Table 2). Injury symptoms were similar to those discussed by Coleman and Seybold (2008b). Callus tissue was also observed around and over the galleries. For example, in February 2009, late instar Agrilus were collected from the outer bark of one specimen of Q. emoryi (61 cm diameter at breast height, DBH, and approximately 30 m tall) that had died recently at Box Canyon in the Santa Rita Mountains (Pima Co.). The tree showed no signs of visible external injury or pathogen infection, and had likely died as a consequence of infestation by A. auroguttatus (i.e., there was no evidence of any predisposing factors). The larvae from this original collection did not complete development, so we could not verify the species at that time, but we suspected that it was A. auroguttatus. We visited the


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Table 1. Chronological presentation of records for Agrilus coxalis and Agrilus auroguttatus from a survey of museum collections and the literature. Date

Locality

Collection

Site Description

Agrilus coxalis undated

Juquila, Mexico

BMNH

undated

Córdova, Mexico

BMNH

undated

BMNH

III-21-1939

Capetillo (Sacatepéquez), Guatemala S. Geronimo (San Jerónimo, Baja Verapaz), Guatemala Tamaulipas, Mexico

FMNH

Santa Engracia

VII-5-1956

Chiapas, Mexico

EMEC

VII-5-1956

Chiapas, Mexico

FSCA

VII-13-1965

Chiapas, Mexico

GHNC

VII-13-1965

Chiapas, Mexico

FSCA

V-11-12-1969

Chiapas, Mexico

CMNC

8.1 km SE San Cristobal de las Casas 5 km SE San Cristobal de las Casas 3.2 km NW Pueblo Nuevo, LLU Bio. Station 21 km NW of Pueblo Nuevo, LLU Bio. Station 16.1 km E Teopisca

V-14-1969 V-17-1969

Chiapas, Mexico Chiapas, Mexico

CMNC CMNC

V-26-1969 V-30-1969


CNCI CNCI

VI-8-1969 VI-5-1974


CNCI CLBC

VII-19-1981 VII-3-5-1986

Veracruz, Mexico Chiapas, Mexico

EMEC CHAH

V-25-1987

Chiapas, Mexico

CLBC

VI-3-6-1989

Zacapa, Guatemala

CHAH

IX-28-1989

Chiapas, Mexico

CSCA

VI-20-1990 VI-21-1990


RHTC FSCA

VII-15-1990 VII-25-30-1990

Jalisco, Mexico Chiapas, Mexico

FSCA TAMU

IX-1-1990 V-24-1991

Chiapas, Mexico Chilasco, Baja Verapaz, Guatemala Zacapa, Guatemala

EBCC CMNC

San Lorenzo, San Marcos, Guatemala Tamaulipas, Mexico Oaxaca, Mexico

CHAH

Jalapa, Veracruz San Cristobal de las Casas, vic. El Chivero, 2438 m elev. 11 km NE San Cristobal de las Casas 12–14 km S San Lorenzo, 305–610 m 10 km E San Cristobal de las Casas 30 km W Comitán Laguna Montebello Parq. Nat., 1524 m elev. 12 km NW Tuito Municipio San Cristobal San Felipe, 2194 m elev. 16 km SO Ocosingo 7.8 km W Chilasco, 1700 m elev. San Lorenzo Rd, 1524–1818 m elev. vic. San Lorenzo, 1768 m

USNM RLWE

16.1 km E Tula, 1189 m elev. 10 km E Mitla, 1890 m elev.

undated

VI-10-1991 VI-10-15-1991 V-10-1994 VII-5-2001

BMNH

FSCA

25.8 km E Teopisca 12.9 km NE San Cristobal de las Casas 6.4 km SE San Cristobal Laguna Montebello Parq. Nat., 1524 m elev. 4.8 km NE San Cristobal 11.3 km SE Teopisca

Notes/Comments/Collector From Waterhouse (1889); Hespenheide (1979), lectotype From Waterhouse (1889); Hespenheide (1979), paratype From Waterhouse (1889); Hespenheide (1979), paratype From Waterhouse (1889); Hespenheide (1979), paratype From J.N. Knull personal collection† G.H. Nelson D.D. Linsdale

G.H. Nelson H.F. Howden (Hespenheide and Bellamy 2009) H.F. Howden H.F. Howden J.M. Campbell In Malaise trap B.V. Peterson C.W. and L.B. O’Brien and G.B. Marshall C. Gold E. Giesbert (Hespenheide and Bellamy 2009) E.G. and T.J. Riley and D.A. Rider E. Giesbert (Hespenheide and Bellamy 2009) R.L. Penrose R.L. Turnbow M. C. Thomas J. E. Wappes R.W. Jones from Malaise trap F.A. Noguera H. and A. Howden J. E. Wappes, 5 specimens E. Giesbert (Hespenheide and Bellamy 2009) Oak forest; J.E. Wappes Beating oak Continued on next page

THE COLEOPTERISTS BULLETIN 65(2), 2011 Table 1.

99

Continued.

Date

Locality

Collection

Olancho, Honduras

FSCA

Montaña del Malacate

Agrilus auroguttatus undated Cochise Co., AZ undated AZ

MCZ FMNH

Palmerlee Huachuca Mts.

VI-16

Cochise Co., AZ

FMNH

VII-26

AZ

CAS

VII-26

Cochise Co., AZ

CAS

VIII-4

Cochise Co., AZ

VIII-15

Cochise Co., AZ

IX-14

AZ

FMNH

VIII-2-1905 VIII-4-1905

AZ Cochise Co., AZ

AMNH USNM

VII-22-1907 VIII-10-1908

AZ AZ

OSU CAS

VIII-15-1940

Pima Co., AZ

CAS

VII-12-1950

AZ

FMNH

VII-15-1953

AZ

FMNH

VII-17-1957

AZ

FMNH

VI-17-1963

Santa Cruz Co., AZ

CIDA

VII-24-1965

Pima Co., AZ

UAIC

VII-6-1968

Pima Co., AZ

FSCA

VII-20-1969 VI-12-1975

Cochise Co., AZ Santa Cruz Co., AZ

FSCA FSCA

Agrilus coxalis V-23-2002

VIII-30-31-1977 Baja California Sur, Mexico

RLWE

Site Description

Notes/Comments/Collector R. Turnbow, 2 female specimens

From J.N. Knull personal collection†, 2 specimens, Chas. Schaeffer co-types Palmerlee, Huachuca Mts. From J.N. Knull personal collection†, determined by C. Schaeffer Santa Rita Mts. From Chamberlain personal collection†; Also in Fisher (1928) Palmerly From Chamberlain personal collection†; catalog #231, paratype Rams (Ramsey) Cn., From Fisher (1928); Huachuca Mts. C. Schaeffer personal collection Palmerlee, Miller Cn., From Fisher (1928); Huachuca Mts. C. Schaeffer personal collection Chiricahua Mts. From J.N. Knull personal collection† Huachuca Mts. “R.C.” [Ramsey Canyon] Palmerlee, Miller Cn., From C. Schaeffer personal Huachuca Mts. collection, 3 specimens, including 1 cotype†, Also noted in Schaeffer (1905), beating black oak branches§ Miller Canyon, Huachuca Mts. H.A. Kaeber Chiricahua Mts. From Van Dyke personal collection† Madera Cn. Foothills, Donated 1962† Santa Rita Mts. Huachuca Mts. From J.N. Knull personal collection†, 3 specimens, including 1 collected on VII-19-1950 Chiricahua Mts. From J.N. Knull personal collection†, 2 specimens Chiricahua Mts. From J.N. Knull personal collection†, 4 specimens Santa Rita Mountains, Madera Canyon, 1706 m † Upper Bear Canyon, Santa Catalina Mts. Bear Canyon, K. Stephan, det. J.N. Knull Santa Catalina Mts. Carr Canyon, Huachuca Mts. G.H. & D.E. Nelson Washington Camp, T23S, K. Stephan, 2 specimens, R16E, S35, Canelo det. G.H. Nelson Hills/Patagonia Mts. (W of Huachuca Mts.) 1 male specimen, beating Sa. Victoria, Sierra de Quercus sp.; Also in La Laguna, trail W of La Westcott (2005) Laguna, 1830 m elev. Continued on next page


100 Table 1.

Continued.

Date

Locality

Agrilus auroguttatus VII-21-2000 Cochise Co., AZ

Collection FSCA

VI-18 to VII-18, Santa Cruz Co., AZ VII-19 to VIII-19-2003 VII-16-30-2004 San Diego Co., CA

CSCA

VI-18-2004

San Diego Co., CA

CSCA

VI-20 to VII-21-2005

Cochise Co, AZ

CHAH

VII-24-2006

San Diego Co., CA

CSCA

VI-27-2008

San Diego Co., CA

CAS

No holdings No holdings

BPBM BYU

No No No No No

LACM SBNM SDMC UCDC UCR

holdings holdings holdings holdings holdings

CHAH

Site Description

Notes/Comments/Collector

Copper Canyon, 1850 m elev., D. Yanega, det. G.H. Montezuma Canyon Rd, Nelson, UCRC ENT 40897 31°21′45″N 110°18′01″W, Huachuca Mts. Upper Madera Canyon F.T. Hovore, I.P. Swift (Hespenheide and Bellamy, 2009) Paco Picacho Campground, Also in Westcott (2005), Cuyamaca State Park 2 specimens Chamber Park, Cuyamaca Also in Westcott (2005) State Park Carr Canyon, 1981 m F.T. Hovore, at bait (Hespenheide and Bellamy 2009) Julian, 4945 Heise Park Road Funnel trap catch with exotic Ips lure Noble Canyon Trailhead, T.W. Coleman, purple Cleveland NF flight intercept traps near Quercus agrifolia Surveyed March 2009 Surveyed March 2009 and April 2010 Surveyed Dec. 2008 Surveyed Jan. 2009 Surveyed Dec. 2008 Surveyed Nov. 2008 Surveyed Dec. 2008

†

These specimens were accessioned under A. auroguttatus. Another specimen from this series is accessioned in the MCZ. This single undated specimen (collected by C. Schaeffer) was from the H.C. Fall collection.

§

same tree on 1–2 May 2009, when additional Agrilus larvae and pupae were collected (Table 2). The outer bark of the tree from the root collar to ∼1.5 m above the forest floor was removed, collected, and returned to the laboratory. These bark samples were placed in emergence cages and monitored daily. As a second example, in October 2009, we collected late instar Agrilus in pre-pupal behavior in the outer bark of a recently dead specimen of Q. hypoleucoides in Miller Canyon, Huachuca Mountains (Cochise Co.). This tree also had similar injury symptoms and larval gallery patterns to those created by A. auroguttatus in CA. No evidence of occurrence of A. auroguttatus was noted on any of the “white” oak species observed in southeastern AZ (i.e., Q. arizonica or Q. grisea). Agrilus auroguttatus was the only phloem/wood borer that emerged from bark samples collected in AZ. A total of 104 adult A. auroguttatus were reared from Q. emoryi bark samples collected in May 2009 from Box Canyon. No adults were reared from Q. hypoleucoides bark samples. In the laboratory, emergence began 13 May and continued until

2 June. Peak emergence for A. auroguttatus in the laboratory occurred on 16 May with 16 adults. Of the 27 A. auroguttatus larvae and pupae that we observed in the bark exterior when we took the samples, four were parasitized (15% parasitism rate). A total of 18 parasitoid larvae were found feeding externally in aggregation on the four A. auroguttatus larvae (Table 3). One of these parasitoids completed development on 3 June 2009, and was described by G. A. P. Gibson (Canadian National Collection of Insects, Agriculture and Agri-Food Canada) as Calosota elongata Gibson (Hymenoptera: Eupelmidae) (Gibson 2010). Additional adult specimens of C. elongata were collected on 6 July (4 specimens), 7 July (3 specimens), 12 July (2 specimens), 13 July (2 specimens), and 14 July, 2009 (1 specimen). These specimens of C. elongata were all female except for one. Seven (six females, one male) additional specimens were collected from the rearing cages when they were dismantled in October 2009. A larger parasitoid (6 adults) also emerged from the bark samples. Its emergence preceded that of A. auroguttatus and began on 6 May 2009; the last adult wasp of

THE COLEOPTERISTS BULLETIN 65(2), 2011 Table 2. Date

Survey locations in southeastern Arizona for oak mortality and activity of Agrilus auroguttatus. Locality

County

GPS Coordinates

XII-2008

Madera Canyon, Santa Rita Mountains

Santa Cruz

N 31.71475° W 110.87559°

II-2009

Box Canyon, Santa Rita Mountains

Pima

N 31.79961° W 110.75921°

II-2009

Carr Canyon, Huachuca Mountains Box Canyon, Santa Rita Mountains

Cochise

N 31.44535° W 110.28618° N 31.79961° W 110.75921°

IX-2009

Miller Canyon, Huachuca Mountains

Cochise

N 31.742687° W 110.25411°

IX-2009

Rucker Canyon, Chiricahua Mountains

Cochise

N 31.74999° W 109.39748°

IX-2009

Chiricahua National Monument, Chiricahua Mountains Pinery Canyon, Chiricahua Mountains Miller Canyon, Huachuca Mountains

Cochise

N 31.00854° W 109.38030°

Cochise

N 31.97136° W 109.34537° N 31.41660° W 110.27461°

Willow Canyon, Santa Catalina Mountains

Pima

V-2009

IX-2009 X-2009 X-2009 †

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Pima

Cochise

N 32.43441° W 110.75285°

Notes/Comments A. auroguttatus injury signs and pupal cells in outer bark on Q. hypoleucoides (61.9 cm DBH†) A. auroguttatus injury signs and Agrilus sp. larvae in outer bark on Q. emoryi, (61.2 cm DBH) D-shaped exit holes and bark staining on Q. hypoleucoides Injury signs, Agrilus sp. larvae, and parasitoids observed in outer bark on Q. emoryi (61.2 cm DBH) Larval galleries and Agrilus sp. larvae in outer bark of Q. emoryi (73.2 cm DBH) Two recently killed Q. emoryi with D-shaped exit holes (54.4 and 38.9 cm DBH) Three recently killed Q. emoryi with D-shaped exit holes and Agrilus sp. larvae (73.4, 52.1, and 73.0 cm DBH) Recently killed Q. emoryi with D-shaped exit holes (60.2 cm DBH) D-shaped exit holes, bark staining, and Agrilus sp. larva in outer bark on Q. hypoleucoides (61.2 cm DBH) Injury signs and Agrilus sp. larvae in outer bark on Q. emoryi (37.6 cm DBH)

DBH, tree diameter at breast height, measured at 1.47 m.

this taxon emerged 18 May 2009. This species was identified as Atanycolus simplex Cresson (Hymenoptera: Braconidae) by Michael J. Sharkey (Department of Entomology, University of Kentucky). Four adult specimens of Temnochila Erichson sp. (Trogossitidae), potential predators, were also collected when the emergence cages were dismantled. During surveys in October 2009, larvae of Trogossitidae and Elateridae were also recovered from beneath the bark of A. auroguttatus-infested Q. emoryi that had died recently in the Huachuca and Chiricahua Mountain Ranges. Each larva was recovered from A. auroguttatus larval galleries or pupal cells in the outer bark. Field Observations in California. Si nce th e original biological observations of A. auroguttatus in CA were reported (Coleman and Seybold 2008b), we report here only additional information on the host range and community of insects associated with this buprestid. In March 2010, we noted adult exit holes and meandering larval galleries on several specimens of Engelmann oak, Quercus engelmannii Greene, on the Descanso Ranger District of the Cleveland National Forest. However, we did not recover larvae or adults of A. auroguttatus from this species of white oak. We also reared several specimens of A. simplex from A. auroguttatus-

infested logs from Q. agrifolia in CA (Table 3), but observed no larval or adult specimens of C. elongata in association with A. auroguttatus in CA. However, a snakefly larva (Agulla Navis, Raphidioptera: Raphidiidae) and a trogossitid larva were each encountered on one occasion while sampling for A. auroguttatus larvae during the dormant season on the Cleveland National Forest at the Pine Creek Trailhead (November 2009; Pine Valley, CA) and William Heise County Park (March 2010; Julian, CA), respectively. Both larvae were found in pupal cells of A. auroguttatus in Q. agrifolia (Table 3).

DISCUSSION Agrilus auroguttatus and A. coxalis are native to North and Central America, and because of the absence of data on these taxa in the economic entomology literature, they appear historically to have presented no significant threat to the health of oak stands in southeastern AZ, Mexico, and Guatemala. These species have been rarely collected in their native regions over the past century. However, A. auroguttatus is currently ubiquitous and abundant within the zone of oak mortality in San Diego Co., CA. Oak mortality was initially

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Table 3. Subcortical insect associates of Agrilus auroguttatus reared or collected from infested Quercus emoryi and Quercus agrifolia bark from survey locations in southeastern Arizona and San Diego Co., California.

Taxon

Likely relationship to A. auroguttatus Host species

Calosota elongata (Hymenoptera: Eupelmidae)

Parasitoid

Q. emoryi

Atanycolus simplex Cresson (Hymenoptera: Braconidae)

Parasitoid

Q. emoryi Q. agrifolia

(Coleoptera: Trogossitidae)

Predator

Q. emoryi Q. emoryi Q. agrifolia

(Coleoptera: Elateridae)

Predator

Q. emoryi

Agulla sp. (Raphidioptera)

Predator

Q. agrifolia

detected on the Descanso Ranger District, Cleveland National Forest and at Cuyamaca Rancho State Park, so the A. auroguttatus infestation is believed to have originated in the vicinity of these two areas. In 2003, the majority of oak mortality was primarily surrounding the communities of Descanso, Guatay, and Pine Valley (Fig. 1). In the following years (2004 to 2008), the zone of oak mortality expanded outward from these communities (Fig. 1). As of fall 2008, neither mortality nor infested trees were present at the U.S.-Mexican border. However, A. auroguttatusinfested trees along the border were detected for the first time in 2009 and infestation rates there are currently very low, suggesting a nascent infestation in this area that is spreading from the north. Increased levels of oak mortality have not been aerially mapped further south of the U.S. and Mexican border, but the spatial pattern of infestation on the U.S. side does not support a range expansion from Mexico. We predict that oak mortality will be evident in northern Baja California, Mexico in the next few years as the infestation spreads south from San Diego Co. Confirmed oak hosts for A. auroguttatus in California have limited distributions in northern Baja California, and do not extend much farther east in San Diego Co. The Mojave and Sonoran Deserts extend from southern Nevada to Sinaloa, Mexico and are dominated primarily by annual species and low shrubs, such as creosote bush, Larrea tridentata (Sessé and Moc. ex DC.) Coville (Zygophyllaceae), and white

Collection date, locality, and observations V-1-2-2009; Box Canyon, AZ; found as ectoparasitoid on mature Agrilus sp. larvae; adult wasps reared later from bark infested with A. auroguttatus V-1-2-2009; Box Canyon, AZ; adult wasps reared from bark infested with A. auroguttatus III-3-2010; W. Heise Co. Park; CA; adult wasps reared from logs infested with A. auroguttatus V-1-2-2009; Box Canyon, AZ; adult Temnochila sp. beetles reared from bark infested with A. auroguttatus X-30-2009; Miller Canyon, AZ; Larval beetles collected from A. auroguttatus larval galleries in outer bark III-3-2010; W. Heise Co. Park, Julian, CA; Larval beetles collected from A. auroguttatus pupal cell in outer bark X-31-2009; Chiricahua National Monument, AZ; Larval beetles collected from A. auroguttatus pupal cell in outer bark XII-30-2009; Pine Valley, CA; Larva collected from pupal cell in outer bark

bursage, Ambrosia dumosa (A. Gray) Payne (Asteraceae) (Shreve and Wiggins 1964). Thus, these deserts geographically isolate the oak hosts, and isolate the population of A. auroguttatus in CA from the native A. auroguttatus populations in southeastern AZ. Because the zone of tree mortality is isolated by the Mohave and Sonoran Deserts to the east and by a band of healthy host type to the south and southeast, and because initial tree mortality was mapped away from the border, we conclude that the hypothesis of continuous range expansion by natural dispersal into CA from AZ and/or Mexico is extremely unlikely. The recent recognition (Hespenheide and Bellamy 2009, Hespenheide et al. 2011) that the CA population is similar morphologically to the AZ population suggests that the tree-killing population of A. auroguttatus in CA originated from AZ. Molecular genetic analyses of these populations are underway to test this hypothesis. The lone collection record of A. auroguttatus in 1977 from southern Baja California (Westcott 2005, Table 1) suggests that either a second introduction has occurred there or that the native range of A. auroguttatus may extend southward in a dispersed fashion into central Mexico on both the Baja Peninsula and the mainland. Native hosts of A. auroguttatus have limited distributions in southeastern AZ and in New Mexico. The native U.S. ranges of Q. emoryi and Q. hypoleucoides are restricted to the southern edge of the Mogollon Rim that bisects AZ and


southwestern New Mexico (USDA Forest Service 2009). The isolated distributions of these oak species may limit the northern edge of the range of A. auroguttatus in AZ. Quercus emoryi and Q. hypoleucoides are also found on several additional mountain ranges in the Coronado National Forest (Dragoon, Galiuro, and Pinaleno) and in southwestern New Mexico, and the distributions of these two oaks also extend south into the northern states of Mexico (Sonora and Chihuahua). Although no collections of A. auroguttatus have been reported from Mexico immediately south of southeastern AZ or from New Mexico immediately east, we suspect that populations may be present in these similar oak savanna habitats. Thus, we speculate that A. auroguttatus is also native to northern Mexico and New Mexico, and further surveys and collecting will be necessary to confirm this hypothesis. The origin and population dynamics of the CA population of A. auroguttatus are topics of intense interest. We hypothesize that A. auroguttatus was introduced into southern CA during the last 10–15 years as a consequence of importation on oak firewood. Firewood movement into southern San Diego Co. from unknown regions within Mexico was reported to have occurred for the last 20 years, and the southern CA zone of tree mortality is a relatively short automobile trip via U.S. Interstate 8 from the oak forests of southeastern AZ (Coleman and Seybold 2008b). Infested firewood could have been imported from southern Baja California, Sonora, or Chihuahua, Mexico, or through vacation traffic from AZ. Firewood movement has been implicated in the transportation of other woodboring tree pests including the emerald ash borer, Agrilus planipennis Fairmaire (Petrice and Haack 2006; Haack et al. 2010), and continues to be a potential threat for moving A. auroguttatus within CA. Because the long-term drought regime and other climatic factors appear to have been similar in both San Diego Co. and southeastern AZ (NOAA 2009), it appears that biotic factors (natural enemies, interspecific competitors, host resistance) may play a greater role in explaining the outbreak in CA and the relatively quiescent level of tree mortality that we noted in southeastern AZ. Both the enemy release and biotic resistance hypotheses have been widely debated as explanations for the successful establishment of invasive species, particularly for invasive plants (Maron and Vilà 2001; Keane and Crawley 2002; Colautti et al. 2004). The near absence of a diverse and coevolved natural enemy complex for A. auroguttatus in CA and the initial discovery and prevalence of C. elongata in AZ (Gibson 2010) support the hypothesis that the invasive population was introduced and may explain, in part, the eruptive behavior of the population in CA. Other eupelmids

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are known to be parasitoids of wood borers, bark beetles, and gall wasps, and similar parasitism levels (18%) were found for larvae of the native bronze birch borer, Agrilus anxius Gory, in areas of the U.S. and Canada (Katovich et al. 2000). Thus, C. elongata may contribute significantly to A. auroguttatus mortality and provide some natural regulation of its host’s population in southeastern AZ. It may also show promise as a biological control agent in CA. Calosota elongata populations were discovered in December 2010 with A. auroguttatus in the Cleveland National Forest, Descanso Ranger District (L. J. Haavik, unpublished data). However, the distribution of this parasitoid appears limited when compared to the expansion of A. auroguttatus in CA and the infestation rate is much lower than what was determined in AZ. Molecular genetic analyses of the populations of C. elongata are also underway in hopes of associating the population sources of the herbivore and parasitoid. Additional research is needed to assess the host specificity and prevalence of C. elongata in AZ. Atanycolus simplex has a broad distribution in the U.S. and has been associated with A. planipennis, the twolined chestnut borer, Agrilus bilineatus (Weber), the elm borer, Saperda tridentata Olivier (Cerambycidae), and various other buprestid and cerambycid species (Quicke and Sharkey 1989; Krischik and Davidson 2007; USDA Forest Service 2010b). Atanycolus simplex has also been associated with the oak cordwood borer, Xylotrechus nauticus (Mannerheim) (Cerambycidae) (Linsley 1964), which emerges frequently from hardwoods throughout CA. Although the single record of A. simplex from A. auroguttatus-infested Q. agrifolia collected in CA (Table 3) could have been associated with X. nauticus, which often also develops in logs such as these, our experience with rearing A. simplex from outer bark of Q. emoryi infested with A. auroguttatus from Pima Co. AZ suggests that A. simplex probably parasitizes A. auroguttatus in CA as well. This braconid appears to have a wider host range and, because of this lack of host specificity, may not be as suitable as C. elongata for augmentative release as a potential biological control agent for A. auroguttatus in CA. Our survey did not reveal any evidence for egg parasitism, so we are not aware if there are any potential differences between AZ and CA. Egg parasitoids are important regulators of populations of other subcortical forest insects. For example, egg parasitism levels of 50% have been reported for A. anxius (Carlson and Knight 1969), and the egg parasitoid Avetianella longoi Siscaro (Hymenoptera: Encyrtidae) has been reported to have a profound impact on the population density of the eucalyptus longhorned beetle, Phoracantha semipunctata (F.)

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(Cerambycidae) (Luhring et al. 2004). Therefore, more intensive surveys for egg parasitoids of A. auroguttatus are needed in both CA and southeastern AZ. Predators such as bark gnawing beetles (Trogossitidae) and click beetles (Elateridae) may also contribute to the natural regulation of A. auroguttatus populations in AZ. A trogossitid and a snakefly larva were both also observed in association with A. auroguttatus in CA. Snakeflies and bark gnawing beetles are generalist predators and commonly prey on bark and wood-boring beetles of pines and hardwoods in the western U.S. (Furniss and Carolin 1977). Differences in interspecific competition may also play a role in the comparative population dynamics of A. auroguttatus in CA and AZ. Evans and Hogue (2004) characterize the patterns of distribution of Coleoptera in CA as influenced by three basic regional faunas: Vancouveran, Southern Sonoran, and Californian. Probably the most relevant regional faunal influence for the biogeography of Agrilus in CA is the Southern Sonoran fauna, which connects the fauna of CA with AZ and northwestern Mexico. Certainly, this is the most relevant when we consider the status of A. auroguttatus in CA. Although the Sonoran faunal elements expanded their ranges northward into CA during the past 10,000 years (Evans and Hogue 2004), apparently CA’s Agrilus fauna did not partake in this range expansion. The Agrilus fauna of CA is relatively depauperate (H. Hespenheide, personal communication), whereas AZ’s fauna is relatively rich. Although we did not encounter them in our survey, in the Chiricahua Mountains, eight species of Agrilus (Agrilus abditus Horn, Agrilus asperulus Waterhouse, Agrilus chiricahuae Fisher, Agrilus geronimoi Knull, Agrilus palmerleei Knull, Agrilus quercicola Fisher, Agrilus quercus Schaeffer, and Agrilus waltersi Nelson) have been collected as adults in association with Quercus L., and Agrilus parkeri Knull has been reared from Q. hypoleucoides (H. Hespenheide, personal communication). There are also species of Chrysobothris (Solier) (Buprestidae) in AZ on oaks that are not present in CA (H. Hespenheide, personal communication). Presumably, some of these would be competitors with A. auroguttatus in AZ if they colonized the same portion of the tree. In CA, the subcortical community of herbivores associated with A. auroguttatus includes oak bark beetles, Pseudopityophthorus Swaine spp., oak ambrosia beetles, Monarthrum Kirsch spp., (both Curculionidae: Scolytinae), the lead cable borer, Scobicia declivis LeConte (Bostrichidae), X. nauticus, and Phymatodes Mulsant spp. (Cerambycidae) (Coleman and Seybold 2008b), as well as Chrysobothris femorata (Olivier) and Chrysobothris wintu Wellso and Manley (Swiecki

and Bernhardt 2006; Wellso and Manley 2007). These species generally colonize oaks after larvae of A. auroguttatus have been well established in the phloem. Thus, in CA there appears to be limited interspecific competition for this niche, whereas in southeastern AZ there is the potential for a wider range of subcortical competitors. Our preliminary observations in CA suggest that A. auroguttatus tends to prefer coast live oak and California black oak (both “red” oaks, subgenus Quercus, section Lobatae [Nixon 1993; Manos et al. 1999]) more than canyon live oak (an intermediate oak species, i.e., neither a red nor a white oak, subgenus Quercus, section Protobalanus) (Coleman and Seybold 2009). Until recently, we had not recorded any observations of injury by A. auroguttatus to Engelmann oak, which is a white oak species (subgenus Quercus, section Quercus) with a limited distribution in southern CA. We attribute the rarity and opportunistic colonization of the non-preferred host Q. engelmannii by A. auroguttatus to the extremely high population density of the beetle in San Diego Co. Two other red oaks in AZ, Q. emoryi and Q. hypoleucoides, are likely native hosts for A. auroguttatus, but we found no evidence that the AZ white oaks, Q. arizonica and Q. grisea, are colonized by A. auroguttatus or any phloem- or wood-boring buprestids. We hypothesize that phloem thickness, bark structure, and/or host chemistry may influence susceptibility to A. auroguttatus. Red oaks in CA or their progenitors may have had a limited coevolutionary relationship with A. auroguttatus and related species, thus rendering them more susceptible to the buprestid than the red oaks in southeastern AZ, whose longer association with A. auroguttatus, and specific bark characteristics and chemistry, may provide some measure of host resistance. White oaks in both CA and AZ appear to have higher levels of host resistance, perhaps associated with their fibrous, furrowed bark and thin phloem (vs. thick, spongy phloem in red oaks). In CA, two additional native red oak species, Shreve oak, Quercus parvula Greene var. shrevei (C.H. Mull.) Nixon, and interior live oak, Quercus wislizenii A. DC, which grow farther north in the state, may also be susceptible to colonization and injury by A. auroguttatus. Two other oaks in CA that are likely to have a more distant coevolutionary relationship with A. auroguttatus are the adventive white oak species, Holm (= Holly) oak, Quercus ilex L., and cork oak, Quercus suber L. These are European species that are widely planted as ornamentals in urban areas of southern CA and the Central Valley. Additional observations and experiments on the physiological host range of A. auroguttatus are needed to test these hypotheses. Agrilus auroguttatus is an intracontinental invasive species that has come to CA. Although it originates


from the same continent as the area of introduction, it is native to a different, but parallel, ecosystem in a different geographic region (concept summarized in Dodds et al. [2010]). We hypothesize that this non-native species is feeding on new hosts in CAwith limited host resistance, filling a vacant niche, and perhaps has a limited ensemble of coevolved insect natural enemies, which would ordinarily regulate the herbivore population. Similarly, in 2003, the soapberry borer, Agrilus prionurus Chevrolat, was first associated with mortality of high-value western soapberry, Sapindus saponaria var. drummondii (Hook. and Arn.) L. D. Benson (Sapindaceae), in Bastrop Co., Texas, and it has since spread to additional counties within the state (Billings and Pase 2008). Agrilus prionurus has also been rarely collected in its native region of Mexico and very little is known about its biology. Other examples of subcortical intracontinental invasive species in the U.S. are the bronze birch borer (Carlos et al. 2002), the locust borer, Megacyllene robiniae (Forster) (Cerambycidae) (Galford 1984), the longhorned beetle Neospondylis upiformis (Mannerheim) (Cerambycidae) (Smith and Hurley 2005), the sixspined ips, Ips calligraphus (Germar) (Wood and Stark 1968) and the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins (both Scolytinae) (Dodds et al. 2010), and the Nantucket pine tip moth, Rhyacionia frustrana (Scudder) (Tortricidae) (Yates et al. 1981). As international examples, the fir bark beetle, Polygraphus proximus Blandford (Scolytinae), has been reported as newly invasive in western Eurasia from its native distribution in the eastern region of the continent (Baranchikov et al. 2010) and the oak splendor beetle, Agrilus biguttatus (F.), has been found recently in Denmark, which is a northward shift in its historic range in central Europe (Pederson and Jørum 2009). The introduction of A. auroguttatus into CA is somewhat unique relative to these other instances of intracontinental invasive species because 1) there is a relatively short distance between the locations of the source and introduction point (approximately 560 km) and 2) there is an apparent relatively extreme susceptibility of the hosts at the introduction point. Most cases of intracontinental invasive species introductions of subcortical forest insects have not led to extensive tree mortality. Human-defined political borders are insignificant when dealing with regions of distinct flora and fauna. Increased trade, nursery stock movement, a changing climate, and firewood movement may lead to additional forest health problems from intracontinental invasive species, and the recent decline of walnut in the U.S. due to thousand cankers disease and the walnut twig beetle, Pityophthorus juglandis Blackman (Scolytinae), may be another manifestation of this problem (Graves et al. 2009, 2010; Seybold et al. 2010).

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The native distributions of the three primary CA hosts of A. auroguttatus extend north through most of the state along the coastal foothills and along the Sierra Nevada (Coleman and Seybold 2009), and oak stands throughout CA are primarily even-aged and dominated by an older size class, which appears to be more susceptible to A. auroguttatus. Firewood movement represents a significant pathway for introducing this species into these regions. The buprestid is currently injuring and killing Quercus spp. between 30 and 1,830 m elevation in southern CA. Previous collection records in its native region extend to 1,981 m elevation (Table 1). Average minimum temperature in the current zone of infestation in San Diego Co. ranges from –12 to –9°C; this range of low temperatures also extends to northern CA along the coast and the lower elevations of the Sierra Nevada mountain ranges (Jordan 2001). These similar mean annual minimum temperatures are also found in southeastern AZ. Thus, this new pest to CA oaks has the potential to impact more northern regions in CA, and the prospect of A. auroguttatus and sudden oak death (caused by the pathogen Phytophthora ramorum Werres, de Cock, and Man [Rizzo and Garbelotto 2003]) acting simultaneously on Q. agrifolia in CA presents a severe threat to this key oak species. As a foundation species of the CA coastal oak savanna, loss of Q. agrifolia may result in “dramatic changes in assemblages of associated species with cascading impacts on food webs and fluxes of energy and nutrients” (Ellison et al. 2010). Thus, A. auroguttatus represents the most significant and aggressive phloem/wood-boring pest of several CA oak species (Swiecki and Bernhardt 2006; Geiger and Woods 2009), and it has the potential to significantly alter California’s landscape by killing many mature trees and impacting the distribution and structure of the fuel load in areas frequently impacted by wildfire. Evans and Hogue (2004) outlined the future of beetle biogeography in CA as a consequence of 1) new discoveries of extant species, 2) natural range extensions of populations currently residing in adjoining states or Mexico, or 3) deliberate or inadvertent introductions of exotic species. Ironically, it appears that A. auroguttatus has enriched the coleopteran fauna of CA as an inadvertent introduction from an adjoining state. This enhancement of biodiversity, however, appears to be accompanied by a rather severe economic consequence for the forests of the state.

ACKNOWLEDGMENTS The authors want to thank Charles L. Bellamy (Plant Pest Diagnostic Laboratory, California Department of Food and Agriculture), Henry A. Hespenheide (Department of Ecology and Evolutionary Biology, University of California-Los

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Angeles), and Richard L. Westcott (Oregon Department of Agriculture), who generously shared their unpublished collection data. HAH and RLW also provided valuable comments on earlier versions of the manuscript. We also thank Michael Sharkey (Department of Entomology, University of Kentucky), Gary A. P. Gibson (Canadian National Collection of Insects, Agriculture and Agri-Food Canada), Joel McMillin and Bobbe Fitzgibbon (USDA Forest Service-Forest Health Protection, Region 3), Andreana Cipollone, Zachary Heath, Andi Koonce (deceased), Meghan Woods, and Paul Zambino (USDA Forest Service-Forest Health Protection, Region 5), Andrew D. Graves (Department of Plant Pathology, University of California-Davis), Steve Heydon and Stacy Hishinuma (Department of Entomology, University of California- Davis), Robert Rabaglia (USDA Forest Service-Forest Health Protection, Washington Office), and the staffs of the Cleveland and Coronado National Forests for their support of and assistance with this work. We thank James Boone (Field Museum of Natural History), Shawn Clark (Monte L. Bean Life Science Museum, Brigham Young University), Lee Herman (American Museum of Natural History), Shepherd Myers (Bernice P. Bishop Museum), Philip Perkins (Museum of Comparative Zoology, Harvard University), Natalia Vandenberg (National Museum of Natural History), and Michael Thomas (Florida State Collection of Arthropods) for generously taking the time to search for and report specimen records from their respective collections (Table 1). Specimens of A. auroguttatus reared from Q. emoryi from AZ were deposited in the CAS, specimens of C. elongata reared from A. auroguttatusinfested bark from AZ were deposited in the CNCI and UCDC, and specimens of A. simplex reared from A. auroguttatus-infested bark or logs were deposited in the UCDC (CA specimens) and the University of Kentucky Insect Collection (HIC) (AZ specimens). Initial critical funding for this work was provided primarily by the USDA Forest Service, Pacific Southwest Research Station, Invasive Species Program, Forest Health Protection, Region 5, and by the Forest Health Monitoring Program (Project # WC-DM-09-01).

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